Method and apparatus for straightening the wire electrode of an electrical discharge machining apparatus

Abstract

An EDM method and apparatus for cutting a workpiece by a wire electrode in the form of a metallic tape or wire, in which the traction exerted on the wire electrode by the mechanism feeding the wire electrode in the machining zone between the wire electrode and the workpiece is modified momentarily, and the variation of machining rate caused by the momentary modification of the force of traction exerted on the wire electrode is detected. The direction in which the machining rate is changed provides an indication of the effect, on the wire electrode, of the transverse forces which deflect the wire in the machining zone, relative to its longitudinal axis. The direction in which the machining rate varies is used to select the direction in which a predetermined machining parameter affecting the transverse forces applied on the wire electrode is changed, such as to maintain the wire electrode properly aligned along its longitudinal axis.

Having thus described the present invention by way of an example of practical application thereof, modification whereof will be apparent to those skilled in the art, what is claimed as new is as follows: 
     
       1. In a method for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of a wire, wherein said wire is displaced relative to said workpiece by being supported by a pair of spaced-apart support and guiding means between which said wire is stretched by a predetermined force of traction applied to said wire, wherein successive voltage pulses are applied across said electrodes for triggering current pulses, and wherein a transverse force is applied to said wire tending to misalign said wire with said support and guiding means, the improvement comprising measuring a signal representing machining efficiency, varying momentarily the predetermined force of traction applied to the wire, measuring the influence exerted by varying said predetermined force of traction upon said signal representing machining efficiency, and adjusting as a function of said last measurement a machining parameter causing said transverse force to be applied on said wire such as to reduce to a minimum value the influence of said variation of force of traction upon said signal representing machining efficiency whereby said machining parameter is adjusted in a direction tending to align said wire with said support and guiding means. 
     
     
       2. The improvement of claim 1 wherein the predetermined force of traction applied on said wire is decreased during a predetermined time interval. 
     
     
       3. The improvement of claim 1 wherein short-circuited discharges during a predetermined time interval are counted as a measure of the influence upon said signal of the variation of the predetermined force of traction applied to said wire. 
     
     
       4. The improvement of claim 1 wherein current pulses are measured during a predetermined time interval as a measure of the influence upon said signal of the variation of the predetermined force of traction applied to said wire. 
     
     
       5. The improvement of claim 1 wherein short-circuited discharges are counted and current pulses are measured during a predetermined time interval as a measure of the influence upon said signal of said variation of the predetermined force of traction applied to said wire. 
     
     
       6. The improvement of claim 3 wherein voltage across the electrodes is the machining parameter which is adjusted. 
     
     
       7. The improvement of claim 3 wherein average machining current is the machining parameter which is adjusted. 
     
     
       8. The improvement of claim 3 wherein voltage across the electrodes and average machining current are the machining parameters which are adjusted. 
     
     
       9. The improvement of claim 4 wherein voltage across the electrodes is the machining parameter which is adjusted. 
     
     
       10. The improvement of claim 4 wherein average machining current is the machining parameter which is adjusted. 
     
     
       11. The improvement of claim 4 wherein voltage across the electrodes and average machining current are the machining parameters which are adjusted. 
     
     
       12. The improvement of claim 5 wherein voltage across the electrodes is the machining parameter which is adjusted. 
     
     
       13. The method of claim 5 wherein average machining current is the machining parameter which is adjusted. 
     
     
       14. The improvement of claim 5 wherein voltage across the electrodes and average machining current are the machining parameters which are adjusted. 
     
     
       15. An apparatus for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of a wire, wherein said wire is displaced relative to said workpiece by being supported by a pair of spaced-apart support and guiding means between which said wire is stretched by a predetermined force of traction applied to said wire and wherein successive voltage pulses are applied across said electrodes for triggering machining current pulses, said apparatus comprising means for obtaining a first signal representative of machining efficiency, means for elaborating a second signal representative of said predetermined force of traction, means for adjusting the force of traction exerted on said wire as a function of said second signal, means for varying said second signal during a predetermined time interval, means for effecting a measure of said first signal before and during said time interval, means for comparing the algebraic resultant of said measures, and means for varying the amplitude of said voltage pulses applied across said electrodes in response to the difference between said measures until said difference reaches a minimum value. 
     
     
       16. An apparatus for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of a wire, wherein said wire is displaced relative to said workpiece by being supported by a pair of spaced-apart support and guiding means between which said wire is stretched by a predetermined force of traction applied to said wire and wherein successive pulses are applied across said electrodes for triggering machining current pulses, said apparatus comprising means for obtaining a first signal representative of machining efficiency, means for elaborating a second signal representative of said predetermined force of traction, means for adjusting the force of traction exerted on said wire as a function of said second signal, means for varying said second signal during a predetermined time interval, means for effecting a measure of said first signal before and during said time interval, means for comparing the algebraic resultant of said measures, and means for varying the average intensity of said machining current pulses flowing across said electrodes in response to the difference between said measures until said difference reaches a minimum value. 
     
     
       17. An apparatus for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of a wire, wherein said wire is displaced relative to said workpiece by being supported by a pair of spaced-apart support and guiding means between which said wire is stretched by a predetermined force of traction applied to said wire and wherein successive voltage pulses are applied across said electrodes for triggering machining current pulses, said apparatus comprising means for obtaining a first signal representative of machining efficiency, means for elaborating a second signal representative of said predetermined force of traction, means for adjusting the force of traction exerted on said wire as a function of said second signal, means for varying said second signal during a predetermined time interval, means for effecting a measure of said first signal before and during said time interval, means for comparing the algebraic resultant of said measures, and means for varying the amplitude of said voltage pulses applied across said electrodes and the average intensity of said machining current pulses in response to the difference between said measures until said difference reaches a minimum value. 
     
     
       18. An apparatus for cutting by electrical discharges an electrode workpiece by means of an electrode tool in the form of a wire, wherein said wire is displaced relative to said workpiece by being supported by a pair of spaced-apart support and guiding means between which said wire is stretched by a predetermined force of traction applied to said wire, wherein successive voltage pulses are applied across said electrodes for triggering machining current pulses, and wherein a transverse force is applied to said wire tending to misalign said wire with said support and guiding means, said apparatus comprising means for measuring a signal representing machining efficiency, means for varying momentarily the predetermined force of traction applied to the wire, means for measuring the influence exerted by varying said predetermined force of traction upon said signal representing machining efficiency, and means for adjusting as a function of said last measurement a machining parameter causing said transverse force to be applied on said wire such as to reduce to a minimum value the influence of said variation of force of traction upon said signal representing machining efficiency, whereby said machining parameter is adjusted in a direction tending to align said wire with said support and guiding means. 
     
     
       19. The apparatus of claim 18 wherein said means for varying momentarily the predetermined force of traction applied to the wire decreases said force of traction during a predetermined time interval. 
     
     
       20. The apparatus of claim 18 wherein said means for measuring the influence of said variation of the predetermined force of traction comprises means for counting short-circuited discharges during a predetermined time interval. 
     
     
       21. The apparatus of claim 18 wherein said means for measuring the influence of said variation of the predetermined force of traction comprises means for measuring current pulses during a predetermined time interval. 
     
     
       22. The apparatus of claim 18 wherein said means for measuring the influence of said variation of the predetermined force of traction comprises means for counting short-circuited discharges and means for measuring current pulses during a predetermined time interval. 
     
     
       23. The apparatus of claim 20 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses. 
     
     
       24. The apparatus of claim 20 wherein said means for adjusting said machining parameter comprises means for adjusting the intensity of said current pulses. 
     
     
       25. The apparatus of claim 20 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses and means for adjusting the intensity of said current pulses. 
     
     
       26. The apparatus of claim 21 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses. 
     
     
       27. The apparatus of claim 21 wherein said means for adjusting said machining parameter comprises means for adjusting the average intensity of said current pulses. 
     
     
       28. The apparatus of claim 21 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses and the average intensity of said current pulses. 
     
     
       29. The apparatus of claim 22 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses. 
     
     
       30. The apparatus of claim 22 wherein said means for adjusting said machining parameter comprises means for adjusting the average intensity of said current pulses. 
     
     
       31. The apparatus of claim 22 wherein said means for adjusting said machining parameter comprises means for adjusting the amplitude of said voltage pulses and means for adjusting the average intensity of said current pulses.